Jesmanowicz Andrzej, Nencka Andrew, Hyde James S
Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Magn Reson Med. 2014 Feb;71(2):846-52. doi: 10.1002/mrm.24713.
A scalable multiband and multichannel digital magnetic resonance imaging system has been developed with the goal of reducing the time needed for acquisition of a single volume of gradient-recalled echo-planar images of the brain.
Transmit pulses are created by an offline computer equipped with a Pentek excitation card (PCIe model 78621) that was built around the Texas Instruments D/A converter (DAC5688).
The spectral purity of pulses made in this way surpasses the quality of pulses made by the standard modulators of the scanner, even when using the same pulse-creation algorithm. There is no need to mix reference waveforms with the magnetic resonance imaging signal to obtain inter-k-space coherency for different repetitions. The key was the use of a system clock to create the Larmor frequency used for pulse formation. The 3- and 4-fold slice accelerations were tested using phantoms as well as functional and resting-state magnetic resonance imaging of the human brain.
Synthesizers with limited modulation-time steps should be replaced not only because of the improved spectral quality of radiofrequency pulses but also for the exceptional coherence of pulses at different slice-selection frequencies.
已开发出一种可扩展的多频段和多通道数字磁共振成像系统，其目标是减少采集单个体积的脑部梯度回波平面图像所需的时间。
发射脉冲由配备Pentek激励卡（PCIe型号78621）的离线计算机生成，该激励卡围绕德州仪器数模转换器（DAC5688）构建。
即使使用相同的脉冲生成算法，以这种方式生成脉冲的频谱纯度也超过了扫描仪标准调制器生成脉冲的质量。无需将参考波形与磁共振成像信号混合以获得不同重复次数下k空间的相干性。关键在于使用系统时钟来生成用于脉冲形成的拉莫尔频率。使用体模以及人脑的功能和静息态磁共振成像测试了3倍和4倍的切片加速。
应更换调制时间步长有限的合成器，这不仅是因为射频脉冲的频谱质量得到了改善，还因为在不同切片选择频率下脉冲具有出色的相干性。
